Retinoic acid (RA), and the combination of TNFα and Interferon (IFN-γ) inhibit human salivary gland tumor (HSG) cell growth with the combination of all three being even more inhibitory (P<0.05). Previous studies have demonstrated that these inhibitory effects of RA, and the combination of TN Fα and IFN-γ are associated with increased accumulation of IGFBP-3 in the culture medium of HSG cells. Therefore, we set out to determine if the increase in IGFBP-3 was due to increased production of IGFBP-3 by the cells and whether IGFBP-3 played a causative role in the inhibition of cellular proliferation. TNFα and IFN-γ induced a rise in IGFBP-3 mRNA levels between 4 and 8 h, which returned to control levels after 24 h. IGFBP-3 was shown to inhibit HSG cell growth at concentrations of >75 U (P<0.05). When antibodies to IGFBP-3 were used with TNFα and IFN-γ, the inhibitory effect of the cytokines on cell growth was diminished. Retinoic acid with TNFα and IFN-γ had a marked inhibitory effect (P<0.05) which was similarly reversed by increasing concentrations of IGFBP-3 antibody. The present data support the hypothesis that the combination of TNFα and IFN-γ with retinoic acid exert their anti-proliferative effect on HSG cells by reducing the mitogenic effect of IGF-I due to a shift in IGF-l from the free to the IGFBP-3-bound form.
- Cancer cells
- Tumor necrosis factor